1. Field of the Invention
The present invention relates to a printing rubber blanket used in an offset printing press or the like.
2. Description of the Related Art
As a printing rubber blanket, one having a surface rubber layer with a smooth surface and a reinforcing layer which is bonded to the surface rubber layer and formed of two to four woven fabrics is known. The printing blanket is used as it is wound around a cylinder.
For example, in printing that uses a lithographic printing rubber blanket, printing ink is applied to a roll-like plate cylinder on which characters and images are formed. The characters and images are transferred onto the smooth rubber surface of the surface layer of a rubber blanket that rotates in tight contact with the plate cylinder. Then, the same characters and images as those on the rubber blanket are transferred onto a sheet surface to obtain a printed product. In printing that uses the rubber blanket, if expansion and shrinkage, i.e., a “shift”, occur on the surface of the rubber blanket, the characters and images on the plate cylinder are not transferred onto the printing sheet correctly.
Jpn. Pat. Appln. KOKAI Publication No.. 7-81267 has the following description. In a printing blanket formed of a support layer including a plurality of woven fabrics, and a surface layer, of the woven fabrics that form the support layer, at least one which is close to the surface layer is formed of a woven fabric in which the warp which is to extend in the rotational direction of a blanket cylinder is formed from polyester mixed yarns. The residual elongation in the warp direction of the woven fabric is set to 20% or more. Then, durability against repeated compression in high-speed printing is increased.
In the printing blanket described in the above reference, when printing pressure is applied, a large shift occurs. Particularly, in printing with a high-speed newspaper press, as the “shift” occurs, the paper feeding ratio (increasing circumference ratio) of the rubber blanket increases, leading to problems such as travel instability of the printing sheet.
According to Jpn. Pat. Appln. KOKAI Publication No. 2000-343852, paragraph [0009], PVA-based fiber is used. In the PVA-based fiber, first recessed and projecting ridges are formed on the fiber surface along the axial direction of the fiber, and second recessed and projecting fine ridges are formed in the first recessed and projecting ridges. This suppresses a shift between fibers, and the dimensional stability of the base fabric is increased.
When recesses and projections are formed in the PVA-based fiber as in Jpn. Pat. Appln. KOKAI Publication No. 2000-343852, the paper feeding ratio (increasing circumference ratio) accompanying a “shift” in printing with the high-speed rotary printing press cannot be controlled to be small. Thus, problems such as travel instability of the sheet are caused.